1. Field of the Invention
The present invention relates to an optical apparatus that deforms a reflecting surface of a mirror, a projection optical system and an exposure apparatus using the optical apparatus, and a method of manufacturing an article.
2. Description of the Related Art
In order to improve the resolution in an exposure apparatus used for manufacturing semiconductor devices or the like, there has been a demand for correcting an optical aberration in a projection optical system in the exposure apparatus. Japanese Patent Laid-Open No. 2005-4146 proposes an optical apparatus that corrects the optical aberration in the projection optical system by deforming a reflecting surface of a mirror included in the projection optical system.
In the optical apparatus described in Japanese Patent Laid-Open No. 2005-4146, the mirror is supported at its peripheral portion by a supporting member, and a plurality of passive actuators and a plurality of active actuators that apply force to the back face (the face on the opposite side of the reflecting surface) of the mirror are provided. The passive actuators are used to correct a mirror shape error with a small shape fluctuation relative to the lapse of time, such as an error caused by a process or assembly of the mirror. On the other hand, the active actuators are used to correct a mirror shape error with a large shape fluctuation relative to the lapse of time, such as an error caused during a time period during which a single substrate is exposed.
Since there is a demand that the exposure apparatus accurately corrects the optical aberration in the projection optical system in real time, the optical apparatus needs to rapidly and accurately deform the reflecting surface of the mirror used in the projection optical system. In order to realize this, the deformation amount of the reflecting surface of the mirror (the sensitivity of the mirror) relative to driving of the actuators may be small, and that drive control can be easily performed. The present inventors have found that, in an optical apparatus in which the center portion of the mirror is fixed to a base plate by a fixing member, the sensitivity of the mirror can be reduced by arranging actuators whose deformation amount at the time of receiving a unit amount of external force is small (i.e., that have a high rigidity), at positions distant from the center of the mirror. The idea of thus reducing the sensitivity of the mirror is not described in Japanese Patent Laid-Open No. 2005-4146.